Thinner

n (1) The portion of a paint, varnish, lacquer, or printing ink, or related product that volatilizes during the drying process. (2) Any volatile liquid used for reducing the viscosity of coating compositions or components; may consist of a simple solvent, or diluent or a mixture of solvents and diluents. (3) Solvents, diluents, low viscosity oils and vehicles added to inks to reduce their viscosity, consistency or tack.